1. Field of the Invention
The present invention relates to interactive exchanges of information between at least one transmitter of audiovisual programs and services and a plurality of terminals linked to said transmitter within a communication network. The invention relates more particularly to a process for controlling the flow of information exchanged.
2. Description of the Prior Art
A structure for exchanging audiovisual information and service information between a transmitter and an interactive terminal generally includes a direct path, via which the interactive audiovisual programs and the services associated therewith are transmitted, and a return path via which one or more terminals can communicate interactively with the said transmitter. The direct path includes, in the case of an analog transmission, a modulator enabling information of the Teletex type for example to be inserted into the frame return lines (VBI: Vertical Blanking Interval) of an analog video signal. In the case of a digital transmission, a multiplexer allows the time-division multiplexing of packets of audio and video data, service data and private data for example according to the MPEG-2 standard.
In the example illustrated in FIG. 1, representing part of a network for exchanging audiovisual and services digital information transmitted by a source S, the direct path is made up of a multiplexer 1, a channel 2 for broadcasting audiovisual programs while the return path is made up of a telephone line 4 linking an interactive terminal 6 to a server 8 intended, on the one hand, for managing a database 10 in which information relating to the users of the interactive terminals are stored, and, on the other hand, for collecting and processing the information output by these terminals during communication with the program source S. The terminals may in particular be television receivers or microcomputers equipped to receive audiovisual programs.
These programs are generally received by a large number of users who may attempt, simultaneously, to establish a communication with the program source S. This results in congestion to the return path 4 and hence to poor usage of the period during which the communications with the source S are authorized. The graph of FIG. 2 represents the number e of tries at establishing communication with the source S as a function of time which are made simultaneously by several users. The capacity R of the network is represented on the ordinate axis by a horizontal bar above which no further call can reach the source S.
Moreover, interactive programs can be broken down into two types of applications: there are, on the one hand, first applications asking users for an almost real-time call (eg. an advertising slot lasting about 30 seconds, thus demanding that the reaction of the users of at least one particular profile be almost immediate) and, on the other hand, second applications for which the calls of the users can be delayed in time on account of the relatively long response time allowed by the program transmitter (eg. "If you would like a brochure, click on yes. Response period: 15 minutes").
Thus beyond a predefined duration starting from an initial reference instant T.sub.0 specific to each application, the calls of the terminals are no longer taken into account by the source S. In point of fact, the various networks are more or less busy, depending on the day's schedules. By way of example, an audiovisual channel with a strong cinematographic component will see its audience increase considerably at the 8.30 p.m. screening if it broadcasts a cinematographic work, while the audience will certainly be smaller at 1 p.m. for the same channel. The aforesaid congestion, following a request, from the program transmitter, asking users to react, may thus form an obstacle to the participation of certain users whose profile is more inclined, for market research reasons for example, to be of interest to said program transmitter. Thus, in the above example, the managers of the channel, by preference targeting the profile of users who enjoy cinematographic works, cannot be certain that they have had the opportunity to transmit a call when the network schedule is busiest.